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<a name="Support-for-testing-link_002dtime-optimizations"></a>
<h3 class="section">7.5 Support for testing link-time optimizations</h3>

<p>Tests for link-time optimizations usually require multiple source files
that are compiled separately, perhaps with different sets of options.
There are several special-purpose test directives used for these tests.
</p>
<dl compact="compact">
<dt><code>{ dg-lto-do <var>do-what-keyword</var> }</code></dt>
<dd><p><var>do-what-keyword</var> specifies how the test is compiled and whether
it is executed.  It is one of:
</p>
<dl compact="compact">
<dt><code>assemble</code></dt>
<dd><p>Compile with <samp>-c</samp> to produce a relocatable object file.
</p></dd>
<dt><code>link</code></dt>
<dd><p>Compile, assemble, and link to produce an executable file.
</p></dd>
<dt><code>run</code></dt>
<dd><p>Produce and run an executable file, which is expected to return
an exit code of 0.
</p></dd>
</dl>

<p>The default is <code>assemble</code>.  That can be overridden for a set of
tests by redefining <code>dg-do-what-default</code> within the <code>.exp</code>
file for those tests.
</p>
<p>Unlike <code>dg-do</code>, <code>dg-lto-do</code> does not support an optional
&lsquo;<samp>target</samp>&rsquo; or &lsquo;<samp>xfail</samp>&rsquo; list.  Use <code>dg-skip-if</code>,
<code>dg-xfail-if</code>, or <code>dg-xfail-run-if</code>.
</p>
</dd>
<dt><code>{ dg-lto-options { { <var>options</var> } [{ <var>options</var> }] } [{ target <var>selector</var> }]}</code></dt>
<dd><p>This directive provides a list of one or more sets of compiler options
to override <var>LTO_OPTIONS</var>.  Each test will be compiled and run with
each of these sets of options.
</p>
</dd>
<dt><code>{ dg-extra-ld-options <var>options</var> [{ target <var>selector</var> }]}</code></dt>
<dd><p>This directive adds <var>options</var> to the linker options used.
</p>
</dd>
<dt><code>{ dg-suppress-ld-options <var>options</var> [{ target <var>selector</var> }]}</code></dt>
<dd><p>This directive removes <var>options</var> from the set of linker options used.
</p></dd>
</dl>




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